Emission Tomography: SPECT and PET
Tomografia por Emissão: SPECT e PET
Cecil Chow Robilotta
Departamento de Física General – Instituto de Física Universidade de São Paulo Rua do Matão, Travessa R, 187 – Cidade Universitária, 05508–900, São Paulo, S.P. – Brasil Tel: (55)(11)3091–6805 Fax: (55)(11) 813–4334. E–mail: cecilcr@if.usp.br
]]> Article received on december 20, 2003
Abstract
Emission tomography is a medical image modality that utilizes molecules labelled with radionuclides, the radiopharmaceuticals, to obtain functional information about specific tissues or systems.
In SPECT, Single Photon Emission Computerized Tomography, the radionuclide decays by emitting one or more photons, while in PET, Positron Emission Tomography, the radionuclide emits a positron, in order to reach a lower energy level. Although the forms of energy emitted are different, the images are reconstructed from the information acquired by external detection of the emitted photons (SPECT) and the pair of annihilation photons (PET) in coincidence.
Due to the specificity and characteristics of these images, their information can be quantified, so that functional or metabolic parameters can be obtained for diagnostic or therapeutic purposes. However, in order to achieve reliable results, factors related to the instrumentation and patient conditions, as well as to the interactions between radiations and tissues and the reconstruction methods have to be considered carefully. In this lecture, after the introduction of the fundamentals of nuclear medicine imaging, the basis of emission tomography acquisition and reconstruction will be presented. Some correction methods will be introduced in order to exemplify the current quantifications adopted in the clinical routine of molecular imaging.
Keywords: Emission tomography, functional imaging, iterative reconstruction, nuclear medicine, PET, quantification, SPECT.
Resumo
]]> Tomografia por emissão é uma modalidade de imagem médica que utiliza moléculas marcadas com radionuclídeos, os radiofármacos, para obter informação funcional sobre tecidos ou sistemas específicos. Em SPECT (Single Photon Emission Computerized Tomography), tomografia por emissão de fóton único, o radionuclídeo decai emitindo um ou mais fótons, enquanto que em PET (Positron Emission Tomography), o radionuclídeo emite um pósitron para alcançar um nível energético mais baixo. Apesar de as formas de energia emitida serem diferentes, as imagens são reconstruídas a partir das informações adquiridas pela detecção externa dos fótons emitidos (em SPECT) e do par de fótons de aniquilação (PET) em coincidência.Devido à especificidade e às características dessas imagens, suas informações podem ser quantificadas, de modo que os parâmetros funcionais ou metabólicos possam ser obtidos para fins de diagnóstico ou terapia. Entretanto, para se conseguir resultados confiáveis, fatores relacionados à instrumentação e às condições do paciente, assim como as interações entre as radiações e tecidos e os métodos de reconstrução, devem ser considerados cuidadosamente. Nesta palestra, após uma introdução aos fundamentos da formação de imagem de medicina nuclear, serão apresentadas as bases da aquisição e da reconstrução tomográfica. Alguns métodos de correção serão introduzidos para exemplificar as quantificações correntemente adotadas na rotina clínica do imageamento molecular.
Palavras–chave: Tomografia por emissão, imageamento funcional, reconstrução iterativa, medicina nuclear, PET, quantificação, SPECT.
DESCARGAR ARTÍCULO EN FORMATO PDF
References
Nuclear Medicine, SPECT, PET:
1. S.R. Cherry, J. Sorenson, M. Phelps, Physics in Nuclear Medicine. USA: W B Saunders, 3rd ed., 2003. [ Links ]
2. I.P.C. Murray, P.J. Ell, Nuclear Medicine in Clinical Diagnosis and Treatment. UK: Churchill Livingstone, 2nd ed., 1998. [ Links ]
3. G.K. von Schulthess, Clinical Molecular Anatomical Imaging: PET, PET/CT and SPECT/CT. USA: Lippincott, Williams & Wilkins, 2002. [ Links ]
4. M.P. Sandler, R.E. Coleman, J.A.Patton, F.J.Th. Wackers, A. Gottschalk, (eds.), Diagnostic Nuclear Medicine. USA: Lippincott, Williams & Wilkins, 2002. [ Links ]
5. P.E. Valk (ed.), D.L. Bailey, D.W. Townsend, M.N. Maisey, Positron Emission Tomography: Basic Science and Clinical Applications. Germany: Springer Verlag, 2003. [ Links ]
6. H.N. Wagner, Z. Szabo, J.W. Buchanan (editors), Principles of Nuclear Medicine. USA: W. B. Saunders, 2nd ed., 1995. [ Links ]
7. R.L. Wahl, J.W. Buchanan, Principles and Practice of Positron Emission Tomography. USA: Lippincott, Williams & Wilkins, 2002. [ Links ]
8. E.E. Camargo, Brain SPECT in Neurology and Psychiatry. J. Nucl. Med., vol.42, no.4, pp.611–623, Apr.2001. [ Links ]
9. D. Delbeke, Oncological Applications of FDG PET imaging. J. Nucl. Med., vol.40, no. 10, pp. 1706–1715, Oct.1999. [ Links ]
10. F.H. Fahey, Data acquisition in PET imaging. J. Nucl. Med. Technol, vol.30, no.2, pp.39–49, Jun.2002. [ Links ]
11. M.W. Groch, W.D. Erwin, Single–Photon Emission Computed Tomography in the year 2001: Instrumentation and quality control. J. Nucl. Med. Technol, vol.29, no. 1, pp. 12–18, Mar.2001 [ Links ]
12. T.G. Turkington, Introduction to PET instrumentation. J. Nucl. Med. Technol, vol.29, no. 1, pp.4–11, Mar.2001. [ Links ]
13. I. Buvat, lecture notes on Nuclear Medicine (in French): [ Links ]
14. http://www.guillemet.org/irene/equipe4/cours.html. [ Links ]
15. S.M. Aoki, "Avaliação de Sistema de Câmaras de Cintilação em Coincidência para Obtenção de Imagens por Emissão de Pósitrons". MSc dissertation (in Portuguese), Instituto de Física da Universidade de São Paulo, São Paulo, Brasil, 2002. [ Links ]
Image Processing and Reconstruction, Medical Image Simulations and Quantification:
1. G. Herman, Image Reconstruction from Projections: Implementation and Applications. Germany: Springer–Verlag, 1979. [ Links ]
2. G. Herman, Image Reconstruction from Projections: The Fundamentals of Computerized Tomography. USA: Academic Press, 1980 [ Links ]
3. A.C. Kak, M. Slaney, Principles of Computerized Tomographic Imaging. USA: IEEE Oress, 1988. [ Links ]
4. M. Ljungberg, M.A. King (editors), Monte Carlo Calculations in Nuclear Medicine: Applications in Diagnostic Imaging. USA: Institute of Physics Publishing, 1998. [ Links ]
5. P.P. Bruyant, Analytic and iterative reconstruction algorithms in SPECT. J. Nucl. Med., vol.43, no. 10, pp. 1343–1358, Oct.2002. [ Links ]
6. I. Buvat, I. Castiglioni, Monte Carlo simulations in SPET and PET. Q. J. Nucl. Med., vol.46, no. 1, pp. 48–61, Mar.2002. [ Links ]
7. L.T. Chang, A method for attenuation correction in radionuclide computed tomography. IEEE Trans. Nucl. Sci. vol.25, no. 1, pp.638–643. 1978. [ Links ]
8. H.M. Hudson, R.S. Larkin, Accelerated image reconstruction using Ordered Subsets of Projection Data. IEEE Trans. Med. Im., vol.13, no.4, pp.601–609, Dec.1994. [ Links ]
9. B.F. Hutton, V. Baccarne, Efficient scatter modelling for incorporation in maximum likelihood reconstruction. Eur. J. Nucl. Med., vol.25, no. 12, pp. 1658–1665, Dec. 1998. [ Links ]
10. P.E. Kinahan, J.G. Rogers, Analytic 3D image reconstruction using all detected events. IEEE Trans. Med. Im., vol.36, no.1, pp. 964–968, Feb. 1989. [ Links ]
11. K. Lange, R. Carson, EM reconstruction algorithms for emission and transmission tomography. J. Comp. Assisted Tomog., vol.8, no.2, pp.306–316, Apr. 1984. [ Links ]
12. Z. Liang, J. Ye, J. Cheng, J. Li, D. Harrington, Quantitative cardiac SPECT in three dimensions: validation by experimental phantom studies. Phys. Med. Biol., vol.43, no.4, pp.905–920, Apr. 1998. [ Links ]
13. J. Radon, On the determination of functions from their integrals along certain manifolds (in German). Math. Phys. Klass., vol.26, 262–277, 1917. [ Links ]
14. C.D. Ramos, Y.E. Erdi, M. Gonen, E. Riedel, H.W.D. Yeung, H.A. Macapinlac, R. Chisin, S.M. Larson, FDG–PET standardized uptake values in normal anatomical structures using iterative reconstruction segmented attenuation correction and filtered back–projection. Eur. J. Nucl. Med., vol.28, no.2, pp. 155–164, Feb.2001. [ Links ]
15. L.A. Shepp, Y. Vardi, Maximum Likelihood reconstruction for emission tomography. IEEE Trans. Med. Im., vol. 1, no.2, pp.113–121, Oct. 1982. [ Links ]
16. D.D. Watson, Quantitative SPECT techniques. Sem. Nucl. Med., vol.29, no.3, pp. 192–203, Jul. 1999. [ Links ]
17. M. Zimny, H.–J. Kaiser, J. Wildberger, B. Nowak, U. Cremerius, O. Sabri, U. Buell, Analysis of FDG uptake with hybrid PET using standardizes uptake values. Eur. J. Nucl. Med., vol.28, no.5, pp.586–592, May 2001. [ Links ]
18. S. Prando," Avaliação dos Efeitos das Correções de Atenuação e Espalhamento na Quantificação de Imagens Cerebrais por SPECT". MSc dissertation (in Portuguese), Instituto de Física da Universidade de São Paulo, São Paulo, Brasil, 2003. [ Links ]
19. A.M.M. Silva, "Reconstrução Quantitativa de SPECT: Avaliação de Correções". PhD thesis (inPortuguese), Instituto de Física da Universidade de São Paulo, São Paulo, Brasil, 1998. [ Links ] ]]>